In, for example, a subterranean petroleum well, isolation of a permeable zone, or isolation between permeable and potential separate zones in the well, may prove essential to be able to control and optimize the course of production from the well. In the process of draining a permeable reservoir and/or weakening existing barriers for isolation between various reservoir zones, fluid streams within the reservoir may change. Such changes may arise by virtue of changing the composition of fluid components in the production stream and/or by virtue of the production stream decreasing or, at worst, ceasing. Further, such changes may arise when a production well extends through a subterranean reservoir and produces oil from an upper oil zone in the reservoir, whereas a lower zone of the reservoir contains water, also referred to as formation water. Usually, the oil will flow into the tubular production string of the well via well perforations formed within the oil zone. As the well production continues and the reservoir is drained for oil, a separating surface between underlying water and overlying oil in the reservoir will move gradually upward within the reservoir. Oftentimes, such a separating surface is referred to as an oil-water contact. Finally, the separating surface will come into contact with, hence in flow communication with, said well perforations, which define the well's influx region from the reservoir. Thereby, water from the reservoir will start to penetrate into the tubular production string via the well perforations and the influx region, which originally was formed exclusively within the oil zone of the reservoir. Thus, an increasingly larger proportion of water will be mixed together with oil during the course of production, whereby the production stream attains a gradually increasing water content during the course of production.
Moreover, if the production stream's pressure drop across the well perforations is of a certain magnitude, so-called water coning of said separating surface (oil-water contact) may arise around the influx region of the well. Such a water coning implies that the separating surface, due to said pressure drop, is lifted up locally around the well perforations. By so doing, water may flow into the well earlier than what would have been the case without such a water coning effect around the influx region of the well. Depending on the physical nature of the reservoir, especially in cases where the reservoir has a relatively low permeability, the oil-water contact of the reservoir may be comprised of a transition zone instead of a relatively sharp separating surface. In such a transition zone, as viewed from below and upward, a gradual transition from primarily water (high water saturation/low oil saturation) to primarily oil (low water saturation/high oil saturation) will exist, whereby the increasing influx of water during the course of production will be more gradual than the case would be when the oil-water contact is comprised of a relatively sharp separating surface.
Gas coning may also arise in a production well, wherein gas from an overlying gas zone may be caused, in a similar manner, to flow prematurely into the well at a particular pressure drop across the perforations of the well in the reservoir.
Both water coning and gas coning involve well-known production-related problems.
Further, a need may exist for isolating two or more permeable zones from each other in a well in order to prevent undesired fluid flow, so-called crossflow, in an annulus in the well. Such permeable zones may exist as adjoining zones, or as separate zones. Typically, said annulus will be an annulus between a pipe string, for example a tubular production string or a tubular injection pipe, and a surrounding borehole wall, i.e. surrounding rocks (formation) defining the borehole wall. In more rare cases, an outer and larger pipe string (pipe body) is used to define an outside of the annulus, whereby the annulus is located between an outer and inner pipe string in the well. Then, a further annulus will exist between the outer pipe string and the borehole wall of the well. Such an outer pipe string is typically used as reinforcement when a production/injection region of a well is located within weak and/or unstable reservoir rocks.
For example, preventing formation water from flowing from a permeable water zone and into a separate, permeable oil zone via such an annulus may be involved in context of such crossflow. It may also involve preventing the formation water from flowing, via the annulus, from the water zone and directly into a production stream from the oil zone. Conversely, it may involve preventing oil from flowing, via such an annulus, from a permeable oil zone and into a separate, permeable water zone. In an injection well, for example a well for injection of water and/or another fluid into a subterranean reservoir, a similar need may exist for isolating one or more permeable zones in the reservoir. By so doing, the injection stream may be conducted into a desired reservoir zone, and via well perforations located vis-à-vis the reservoir zone. As such, it may involve conducting an injection water stream into, or in vicinity of, a permeable oil zone in a subterranean reservoir, thereby increasing the reservoir pressure and forcing more oil out of the reservoir. In context of such a course of injection, it is also possible to construe that a need may arise for moving the injection stream to one or more other permeable zones in the reservoir, for example to zones in, or in vicinity of, the oil zone of the reservoir. As such, a need may arise for isolating previous injection zones and replacing these with new injection zones in the reservoir. In such cases, too, isolation of a permeable zone, or isolation between various permeable zones, may prove essential to be able to control and optimize the course of injection in such a well.
A well barrier, for example a cement barrier, the purpose of which is to prevent said undesired fluid flow (crossflow) in an annulus between various permeable zones in a well, may also be exposed to large strains, i.a. in the form of substantial pressure- and temperature differences. As such, the well barrier may be exposed to violent forces, including tensile-, compressive- and torsional forces. It is known that such strains over time may cause damage to such a well barrier, whereby the integrity of the barrier, hence its isolation effect, is destroyed completely or partially. Thus, such undesired fluid flow (crossflow) may arise in annuli behind, for example, casings, liners, production pipes and injection pipes. This may reduce or render impossible, in the worst case, further production from, or possibly injection into, a subterranean well.